Method of evaluating cleanliness, method of determining cleaning condition, and method of manufacturing silicon wafer

ABSTRACT

A method of evaluating cleanliness of a member having a silicon carbide surface, the method including bringing the silicon carbide surface into contact with a mixed acid of hydrofluoric acid, hydrochloric acid and nitric acid; concentrating the mixed acid brought into contact with the silicon carbide surface by heating; subjecting a sample solution obtained by diluting a concentrated liquid obtained by the concentration to quantitative analysis of metal components by Inductively Coupled Plasma-Mass Spectrometry; and evaluating cleanliness of the member having a silicon carbide surface on the basis of a quantitative result of metal components obtained by the quantitative analysis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.16/087,879, filed Sep. 24, 2018, which is the U.S. National Stage ofPCT/JP2017/007749, filed Feb. 28, 2017, which claims priority to JPApplication No. 2016-064071, filed Mar. 28, 2016. The disclosure of eachof these applications is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a method of evaluating cleanliness, amethod of determining a cleaning condition, and a method ofmanufacturing a silicon wafer. Specifically, the present inventionrelates to a method of evaluating cleanliness of a member having asilicon carbide surface, a method of determining a cleaning condition ofa member having a silicon carbide surface, and a method of manufacturinga silicon wafer.

BACKGROUND ART

It is generally said that silicon carbide (SiC) is a material excellentin heat resistance, chemical durability and the like. Accordingly,silicon carbide is widely used as a material constituting variousmembers in various types of technical fields. As an example, in a fieldof manufacturing a silicon wafer (hereinafter, also referred to as a“wafer”), coating, with silicon carbide, a surface of an internal member(such as a heat-shielding member) of a lifting machine to be used inmanufacturing a single crystal silicon ingot that is sliced to give asilicon wafer or a surface of a member for placing a silicon wafer (suchas a susceptor or a wafer boat) in heat treatment; constituting thewhole member from silicon carbide; or the like is being performed. Inthe following, a member whose surface is at least partially made ofsilicon carbide, that is, a member having at least partially a siliconcarbide surface (SiC surface) is described as a “silicon carbide-basedmember.”

With respect to a silicon carbide-based member, a silicon carbide-basedmember is cleaned for the reduction of metal contamination from thesilicon carbide-based member (refer to, for example, Japanese UnexaminedPatent Publication (KOKAI) No. 2010-4073 and Japanese Unexamined PatentPublication (KOKAI) No. 2000-169233, which are expressly incorporatedherein by reference in their entirety).

SUMMARY OF THE INVENTION

For example, with respect to a silicon wafer, metal contamination of asilicon wafer is required to be lowered since the contamination affectsproperties of a device to be produced using the wafer. A cause of themetal contamination of a silicon wafer includes the fact that, as aresult of metal contamination of a member coming into contact with awafer during a manufacturing process of a single crystal silicon ingotor a silicon wafer, the metal element diffuses from the member into theatmosphere and is incorporated into the single crystal silicon ingot orthe silicon wafer, or a silicon wafer is metal-contaminated as aconsequence of contact of the wafer with the member. Accordingly, in aprocess for manufacturing a silicon wafer including a process using asilicon carbide-based member, it is desirable to clean a siliconcarbide-based member to thereby lower metal contamination of the siliconcarbide-based member. Furthermore, it is more desirable to evaluatecleanliness as to whether or not a silicon carbide-based member is in astate where metal contamination has sufficiently been reduced andcleaned by the cleaning, and to examine the change or the like of acleaning condition if the cleanliness is insufficient. A method ofevaluating cleanliness of a silicon carbide-based member for thispurpose requires the capability of highly accurately evaluating metalcontamination of a silicon carbide-based member.

An aspect of the present invention provides for a means for highlyaccurately evaluating metal contamination of a silicon carbide-basedmember.

An aspect of the present invention relates to a method of evaluatingcleanliness of a member (silicon carbide-based member) having a siliconcarbide surface, the method including:

bringing the silicon carbide surface into contact with a mixed acid ofhydrofluoric acid, hydrochloric acid and nitric acid;

concentrating the mixed acid brought into contact with the siliconcarbide surface by heating;

subjecting a sample solution obtained by diluting a concentrated liquidobtained by the concentration to quantitative analysis of metalcomponents by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS); and

evaluating cleanliness of the member having a silicon carbide surface onthe basis of a quantitative result of metal components obtained by thequantitative analysis.

In an embodiment, in the mixed acid, a concentration of hydrofluoricacid ranges from 5 to 15 mass %, a concentration of hydrochloric acidranges from 5 to 15 mass %, and a concentration of nitric acid rangesfrom 5 to 15 mass %.

In an embodiment, the sample solution is prepared by diluting theconcentrated liquid obtained by the concentration through the additionof hydrofluoric acid and hydrogen peroxide.

In an embodiment, the member having a silicon carbide surface is amember for manufacturing a silicon wafer.

In an embodiment, the member for manufacturing a silicon wafer is asusceptor.

A further aspect of the present invention relates to a method ofdetermining a cleaning condition of a member having a silicon carbidesurface, the method including:

cleaning a silicon carbide surface of a member having a silicon carbidesurface under a candidate cleaning condition;

evaluating cleanliness of the member having a silicon carbide surfaceafter the cleaning by the above method of evaluating cleanliness; and

determining a candidate cleaning condition under which the cleanlinesshas been determined to be within an allowable level as a result of theevaluation, as a cleaning condition of a member having a silicon carbidesurface in an actual manufacturing process of a silicon wafer.

A further aspect of the present invention relates to a method ofmanufacturing a silicon wafer, including:

determining a cleaning condition by the above method of determining acleaning condition;

cleaning a member for manufacturing a silicon wafer having a siliconcarbide surface under the determined condition; and

manufacturing a silicon wafer through a manufacturing process includinga process using the cleaned member for manufacturing a silicon wafer.

A further aspect of the present invention relates to a method ofmanufacturing a silicon wafer, including:

evaluating cleanliness of a member for manufacturing a silicon waferhaving a silicon carbide surface by the above method of evaluatingcleanliness; and

manufacturing a silicon wafer through a manufacturing process includinga process using a member for manufacturing a silicon wafer, whosecleanliness has been determined to be within an allowable level as aresult of the evaluation.

According to an aspect of the present invention, it becomes possible tohighly accurately evaluate metal contamination of a member having asilicon carbide surface (silicon carbide-based member).

DESCRIPTION OF EMBODIMENTS

[Method of Evaluating Cleanliness]

An aspect of the present invention relates to a method of evaluatingcleanliness of a member having a silicon carbide surface (siliconcarbide-based member), the method including: bringing the siliconcarbide surface into contact with a mixed acid of hydrofluoric acid,hydrochloric acid and nitric acid; concentrating, by heating, the mixedacid brought into contact with the silicon carbide surface; subjecting asample solution obtained by diluting a concentrated liquid obtained bythe concentration to quantitative analysis of metal components byInductively Coupled Plasma-Mass Spectrometry (ICP-MS); and evaluatingcleanliness of the member having a silicon carbide surface on the basisof a quantitative result of metal components obtained by thequantitative analysis, (hereinafter, the above method is also referredto simply as a “method of evaluating cleanliness”).

In the present invention and present description, “cleanliness” means adegree of metal contamination. The method of evaluating cleanlinessaccording to an aspect of the present invention makes it possible tohighly accurately evaluate cleanliness of a silicon carbide-basedmember. The present inventors presume that the facts that: the mixedacid can recover, at a high recovery rate, metal components from asilicon carbide-based surface; the mixed acid having recovered, at ahigh recovery rate, metal components from the silicon carbide-basedsurface is concentrated by heating; and quantitative analysis isperformed with ICP-MS that is a highly sensitive analysis apparatus,contributes to the reason why high-accurate evaluation becomes possible.However, the above is presumption, and does not limit the presentinvention at all.

Hereinafter, the method of evaluating cleanliness will be explained inmore detail.

<Evaluation-Target Member>

An evaluation target of the method of evaluating cleanliness is a memberhaving a silicon carbide surface (silicon carbide-based member). Thesilicon carbide surface means a surface constituted of silicon carbide.In a member having a silicon carbide surface, the whole or a part of thesurface of the member is a silicon carbide surface. The member having asilicon carbide surface is, in an embodiment, a member whose surface isat least partially, that is, partially or wholly covered with siliconcarbide; in another embodiment, a member that is wholly made of siliconcarbide; and, furthermore, in other embodiments, a member that ispartially made of silicon carbide and the part composed of siliconcarbide is exposed to a part of the surface of the member. In a siliconcarbide-based member having silicon carbide as a covering layer thatcovers at least a part of a member, a thickness of the covering layer isnot particularly limited. In addition, a size and a shape of a siliconcarbide-based member that is an evaluation target are also notparticularly limited.

For example, when a manufacturing process of a silicon wafer is taken asan example, a silicon carbide-based member is widely used as a memberfor manufacturing a silicon wafer. Examples of silicon carbide-basedmembers for manufacturing a silicon wafer can include: an internalmember (such as a heat-shielding member) of a lifting machine to be usedin manufacturing a single crystal silicon ingot; a susceptor (awafer-placing member); a lift pin of a susceptor; a boat in a heattreatment furnace or CVD (Chemical Vapor Deposit) furnace; and the like,and evaluation of cleanliness of these various members can be performedby the method of evaluating cleanliness according to an aspect of thepresent invention. However, evaluation-target members in the method ofevaluating cleanliness according to an aspect of the present inventionare not limited to members for manufacturing a silicon wafer. If theseare members having a silicon carbide surface (silicon carbide-basedmembers), it is possible to set, as evaluation targets, siliconcarbide-based members to be used not only in a field of manufacturing asilicon wafer, but also in various fields.

According to the examination by the present inventors, recovery of metalcomponents from a silicon carbide surface is more difficult thanrecovery of metal components from a silicon wafer surface. With respectto the reason thereof, although the following is only presumption, thepresent inventors presume that one cause is a rougher surface of asilicon carbide than a surface of a silicon wafer. For example, SRc(average peak height of roughness curved surface) of a silicon carbidesurface can be equal to or higher than 1.00 μm (for example,approximately 1.00 to 10.00 μm), and SPc (average peak height ofcross-section curved surface) thereof can be equal to or higher than1.00 μm (for example, approximately 1.00 to 10.00 μm). Here, the SRc isa value to be measured by the method specified in JIS B 0601-2001, andthe SPc is a value to be measured by the method specified in ISO 25178.

<Mixed Acid>

In the method of evaluating cleanliness, the silicon carbide surface ofa silicon carbide-based member being an evaluation target is broughtinto contact with a mixed acid of hydrofluoric acid (HF), hydrochloricacid (HCl) and nitric acid (HNO₃). In the following, the mixed acid isalso described as a “recovery liquid.” The recovery liquid containingthe above three kinds of acids can recover metal components adhering toa silicon carbide surface, that is, can incorporate metal componentsadhering to a silicon carbide surface into the recovery liquid, at ahigh recovery rate. This point was newly found out as the result of keenexaminations by the present inventors.

As to concentrations of the three kinds of acids contained in the mixedacid, the concentration of hydrofluoric acid ranges preferably from 5 to15 mass % and more preferably from 5 to 10 mass %, the concentration ofhydrochloric acid ranges preferably from 5 to 15 mass % and morepreferably from 10 to 15 mass %, and the concentration of nitric acidranges preferably from 5 to 15 mass % and more preferably from 10 to 15mass %. The mixed acid can preferably be an aqueous solution of theabove three kinds of acids.

Contact of the mixed acid with a silicon carbide surface can beperformed by a known contact method such as a method of immersing amember having a silicon carbide surface (silicon carbide-based member)into the mixed acid, a method of scanning the mixed acid onto a siliconcarbide surface, or the like. An amount of the mixed acid to be usedhere is not particularly limited, and the mixed acid having an amountsuitable for the contact method may be used. Furthermore, contact of themixed acid with a silicon carbide surface can be performed, for example,under the atmospheric pressure and at room temperature (for example,approximately 15 to 25° C.), and the mixed acid can be used withouttemperature control (heating or cooling).

<Preparation of Sample Solution>

As a consequence of contacting a silicon carbide surface with the mixedacid as described above, metal components adhering to a silicon carbidesurface can be recovered into the mixed acid. However, it is consideredthat, when the mixed acid having recovered metal components is directlyintroduced into ICP-MS, interference with a mass number of anevaluation-target metal is induced, whereby decrease in quantitativeaccuracy, sensitivity reduction, apparatus deterioration, and the likeare caused. Accordingly, in the above method of evaluating cleanliness,a sample solution having been prepared as follows is subjected toquantitative analysis of a metal component by ICP-MS. The presentinventors consider that this point also contributes to allowinghigh-accurate evaluation.

(Heating Concentration)

For preparing a sample solution, first, the mixed acid brought intocontact with a silicon carbide surface is heated for concentration.Heating can be performed by a known method for concentrating solution byheating such as a method of heating, on a hot plate, a vessel (such as abeaker) containing the mixed acid brought into contact with a siliconcarbide surface. Concentration by heating is preferably performed so asto allow liquid to remain without complete drying and solidification.The amount of liquid allowed to remain can be set to, for example,approximately 10 to 50 μL. Among metal components, there is a metalcomponent that volatilizes due to complete drying and solidification,and thus it is preferable to allow liquid to remain without performingcomplete drying and solidification in order to make quantitativedetermination of such metal components possible. A liquid amount of themixed acid (mixed acid amount) before concentration is, for example,approximately 5000 to 1000 μL, but, as described above, a mixed acidamount to be brought into contact with a silicon carbide surface is notparticularly limited. Therefore, the amount may be larger or smallerthan the above range.

(Dilution)

After that, a concentrated liquid obtained by the concentration isdiluted, whereby a sample solution to be introduced into ICP-MS isprepared. Various kinds of dilute acids known as a dilute acid capableof being introduced into ICP-MS can be used for the dilution. Here,“dilute acid” means an acid solution (for example, an aqueous solution)in which a concentration of a contained acid (in a case where pluralacids are contained, each concentration of each of these acids) is lessthan 3 mass %. Examples of preferable dilute acids can include a mixedacid of hydrochloric acid and hydrogen peroxide (HCl/H₂O₂), dilutenitric acid (dilute HNO₃), and the like. Here, the concentration of eachacid can be, for example, approximately 1 to 3 mass %. A dilution ratiomay be suitably determined by the amount of a concentrated liquid beforedilution. As an example, on a volume basis, the dilution ratio can beset to approximately 20 to 100 times relative to an amount of aconcentrated liquid before the dilution. The dilution ratio here meansthat, for example, a dilution ratio is 20 times when the amount ofliquid obtained by dilution is 20 times the amount of a concentratedliquid before the dilution, on a volume basis.

<Quantitative Analysis>

The sample solution obtained as described above is subjected toquantitative analysis of metal components by ICP-MS. ICP-MS is ananalysis method that can quantitatively analyze metal components withhigh sensitivity. It becomes possible to highly accurately evaluatecleanliness by subjecting the sample solution to quantitative analysisby ICP-MS. Usually, in ICP-MS, a sample solution is gasified oraerosolized with a nebulizer, which is then introduced into argon plasmagenerated by high-frequency power applied with an inductively-coupledcoil. The sample is heated to approximately 6000 to 7000 K inatmospheric pressure plasma, and each element is atomized, andfurthermore, ionized with an efficiency of usually equal to or higherthan 90%. Ions pass through a skimmer (interface), are thenenergy-focused by an ion lens part, and subsequently are introduced intoa mass spectrometer maintained at a high-vacuum state of, for example,<10⁻⁶ Pa to thereby be subjected to mass analysis. Accordingly, metalcomponents in the sample solution can be quantified. Quantitativeanalysis of metal components by ICP-MS can be performed using acommercially available ICP-MS or an ICP-MS having a known configuration.ICP-MS can quantitatively analyze various metal components. Specificexamples of metal components (metal elements) to be quantitativelyanalyzed can include Na, Al, Cr, Fe, Ni, Cu, Mo, W, Ti, Nb, Ta, K, Ca,Zn, Co, Mg, Mn, Li, Sr, Ag, Pb, V, Ba and the like.

The larger amount of metal components contained in the sample solutionmeans that the silicon carbide surface being an evaluation target wasmore contaminated with the metal components, namely, had lowercleanliness. Accordingly, cleanliness of a silicon carbide surface beingan evaluation target can be evaluated on the basis of a quantitativeresult by ICP-MS. The evaluation of cleanliness may be given as a degreeof contamination by a specified metal component, or be given on thebasis of the sum of contamination amounts by metal components of equalto or more than two kinds.

[Method of Determining Cleaning Condition]

The method of evaluating cleanliness as described above can be used, inan embodiment, for determining a cleaning condition of a member having asilicon carbide surface.

That is, an aspect of the present invention relates to a method ofdetermining a cleaning condition of a member having a silicon carbidesurface, the method including:

cleaning a silicon carbide surface of a member having a silicon carbidesurface under a candidate cleaning condition;

evaluating cleanliness of the member having a silicon carbide surfaceafter the cleaning by the above method of evaluating cleanliness; and,

determining a candidate cleaning condition under which the cleanlinesshas been determined to be within an allowable level as the result of theevaluation, as a cleaning condition of a member having a silicon carbidesurface in an actual manufacturing process of a silicon wafer. Accordingto the above method of evaluating cleanliness, cleanliness of a memberhaving a silicon carbide surface (silicon carbide-based member) can behighly accurately evaluated. The above method of determining a cleaningcondition makes it possible, by determining, on the basis of theevaluation result, whether or not a candidate cleaning condition issuitable as a cleaning condition in an actual manufacturing process, touse a silicon carbide-based member considered to give high cleanlinessby the cleaning in the actual manufacturing process. In addition,accordingly, metal contamination of a silicon wafer by a siliconcarbide-based member can be suppressed in the actual manufacturingprocess.

Examples of cleaning conditions of a silicon carbide-based member caninclude a composition of a cleaning liquid, cleaning time, number ofcleaning times, and the like. In a case where an evaluation result(cleanliness) obtained through evaluation of a silicon carbide-basedmember cleaned under a certain candidate cleaning condition, by theabove method of evaluating cleanliness, is within an allowable level,the candidate cleaning condition can be determined as a cleaningcondition of a silicon carbide-based member in an actual manufacturingprocess of a silicon wafer. The allowable level here is not particularlylimited, and can be determined on the basis of cleanliness required fora silicon wafer in accordance with the intended use or the like of thesilicon wafer. On the other hand, in a case where an evaluation result(cleanliness) obtained through evaluation of a silicon carbide-basedmember cleaned under a certain candidate cleaning condition, by theabove method of evaluating cleanliness, exceeds an allowable level, thecleaning condition can be determined not to be applicable as a cleaningcondition in an actual manufacturing process. In this case, it is alsopossible to modify the cleaning condition and determine a new candidatecleaning condition, and to perform evaluation with respect to thecandidate cleaning condition. Furthermore, it is also possible todetermine a cleaning condition of a silicon carbide-based member in anactual manufacturing process of a silicon wafer, by repeatingdetermination and evaluation of such a new candidate cleaning condition.

Examples of silicon carbide-based members being cleaning targets caninclude various members exemplified above as members for manufacturing asilicon wafer. Furthermore, examples of silicon wafers to bemanufactured in an actual manufacturing process can include, in additionto a so-called bare wafer, various silicon wafers such as a siliconepitaxial wafer having an epitaxial layer on a silicon substrate and asilicon wafer having a thermal oxide film as an outermost layer.Manufacturing processes of these silicon wafers are known.

[Method of Manufacturing Silicon Wafer]

A further aspect of the present invention relates to a method ofmanufacturing a silicon wafer, including:

determining a cleaning condition by the above method of determining acleaning condition;

cleaning a member for manufacturing a silicon wafer having a siliconcarbide surface under the determined cleaning condition; and

manufacturing a silicon wafer through a manufacturing process includinga process using the cleaned member for manufacturing a silicon wafer.(Hereinafter, the above method is referred to as a “manufacturing method1.”)

A further aspect of the present invention relates to a method ofmanufacturing a silicon wafer, including:

evaluating cleanliness of a member for manufacturing a silicon waferhaving a silicon carbide surface, by the above method of evaluatingcleanliness; and

manufacturing a silicon wafer through a manufacturing process includinga process using a member for manufacturing a silicon wafer, whosecleanliness has been determined to be within an allowable level as aresult of the evaluation. (Hereinafter, the above method is referred toas a “manufacturing method 2.”)

According to the manufacturing method 1, it is possible to manufacture asilicon wafer by the use of a silicon carbide-based member (member formanufacturing a silicon wafer) cleaned under a cleaning conditiondetermined by the above method of determining a cleaning condition. Thecleaning condition determined by the above method of determining acleaning condition is a cleaning condition under which the capability ofproviding a silicon carbide-based member having a high cleanliness bythe cleaning has been confirmed. As a consequence of using a siliconcarbide-based member cleaned under the cleaning condition, it becomespossible to manufacture a silicon wafer with reduced metalcontamination.

According to the manufacturing method 2, it is possible to manufacture asilicon wafer by the use of a silicon carbide-based member (member formanufacturing a silicon wafer) whose cleanliness has been confirmed asbeing high by the above method of evaluating cleanliness. Accordingly,it becomes possible to manufacture a silicon wafer with reduced metalcontamination. An allowable level in the manufacturing method 2 is alsonot particularly limited, and can be determined on the basis ofcleanliness required for a silicon wafer in accordance with the intendeduse of the silicon wafer.

Examples of members for manufacturing a silicon wafer in themanufacturing method 1 and the manufacturing method 2 can includevarious members exemplified above as members for manufacturing a siliconwafer. Examples of processes using the member can include various heattreatments such as a heat treatment for forming an epitaxial layer(vapor phase growth). In the heat treatment, a silicon wafer is placedon, for example, a member for manufacturing a silicon wafer (such as asusceptor and various kinds of boats as described above), and, at thistime, the silicon wafer comes into contact with the member formanufacturing a silicon wafer. In addition, a lift pin of a susceptorcomes into contact with a surface of a silicon wafer when it lifts thesilicon wafer placed on the susceptor. Here, when the member formanufacturing a silicon wafer is metal-contaminated, the metal componentadheres to the silicon wafer to thereby contaminate the silicon wafer.In addition, as a consequence of diffusion of an adhering metalcomponent into the inside of the silicon wafer due to a heat treatment,the silicon wafer may also be metal-contaminated. In the manufacturingmethod 1 and the manufacturing method 2, for example, it is possible toreduce metal contamination of a silicon wafer which is generated in thisway. As described above, a manufacturing process of a silicon wafer isknown. In the manufacturing method 1 and the manufacturing method 2, asilicon wafer can be manufactured by a known manufacturing process.

EXAMPLES

Hereinafter, the present invention will be further explained on thebasis of Examples. However, the present invention is not limited toembodiments shown in Examples. “%” described below means “mass %.” Thefollowing processes and evaluations were performed under the atmosphericpressure and at room temperature (approximately 15 to 25° C.) and themixed acid was used without temperature control (heating or cooling)unless otherwise noted.

1. Contamination of Silicon Carbide-Based Member with Metal Having KnownConcentration

A susceptor of a commercially available vapor-phase growth apparatus wassubjected to a contamination treatment with a metal having a knownconcentration. The susceptor is a susceptor in which the whole surfaceof a carbon base material is covered with silicon carbide. The metalcontamination treatment was performed by dropping a liquid containing ametal component having a known concentration onto a surface of thesusceptor, and then by drying the liquid.

For the purpose of the following evaluations, plural susceptorssubjected to a contamination treatment with a metal having a knownconcentration were prepared in the same way.

2. Recovery of Metal Component by Contact of Silicon Carbide Surfacewith Mixed Acid

As a consequence of scanning (contacting) about 5000 to 10000 μL ofvarious kinds of mixed acids on the silicon wafer-placing surface(silicon carbide surface) of the susceptor subjected to thecontamination treatment with a metal having a known concentration, ametal component adhering to the placing surface was recovered with amixed acid. Mixed acids (recovery liquids) used were as follows:

mixed acid of hydrofluoric acid and nitric acid (HF (2%)/HNO₃ (2%))[Comparative Example],

mixed acid of hydrofluoric acid, hydrochloric acid, and hydrogenperoxide (HF (4%)/HCl (3%)/H₂O₂ (3%)) [Comparative Example], and

mixed acid of hydrofluoric acid, hydrochloric acid and nitric acid (HF(8%)/HCl (12%)/HNO₃ (14%)) [Example].

Each of the mixed acids is an aqueous solution containing the acids asacid components and containing each acid in the concentration.

3. Concentration by Heating and Dilution of Recovered Liquid

The mixed acid (the recovery liquid) brought into contact with thesilicon wafer-placing surface (silicon carbide surface) of the susceptorin the 2. was put in a beaker and was then heated on a hot plate (settemperature: 300° C.) to thereby be concentrated to a liquid amount ofabout 30 μL. A mixed acid of hydrofluoric acid and hydrogen peroxide(aqueous solution of hydrofluoric acid concentration 2% and hydrogenperoxide concentration 2%) was added to a beaker containing theconcentrated liquid obtained by the concentration, and the liquid amountof the resultant diluted liquid was 1000 μL.

4. Quantitative Analysis of Metal Components by ICP-MS (1)

A sample solution obtained by the dilution in the 3 was introduced intoan Inductively-Coupled Plasma Mass Spectrometer (ICP-MS) andquantitative analysis of metal components was performed.

The contamination amount of a known concentration in the 1. was set to100%, and each metal component amount determined quantitatively byICP-MS relative to the contamination amount of a known concentration wascalculated as a recovery rate.

Table 1 below shows quantitative analysis results (recovery rates,average of recovery rates, and variation) obtained by performing theprocesses of the 2. to 4. twice to the suscepter treated by metalcontamination of known concentration in the 1, as to each metalcomponent. The variation was obtained as: variation={(maximumvalue−minimum value)/average value}×100/2. Variations shown in Tables 2and 3 are also values calculated in the same way.

TABLE 1 Mixed acid Metal to be quantitatively analyzed Na Al Cr Fe Nl CuComparative Example HF/HNO₃ Recovery rate (1)/%  72 78 71 74 73 70Recovery rate (2)/%  91 93 86 87 87 86 Average recovery  82 86 79 81 8078 rate/% Variation  11.656442 8.771930 9.554140 8.074534 8.75000010.256410 Comparative Example HF/HCl/H₂O₂ Recovery rate (1)/% 100 96 9699 92 94 Recovery rate (2)/%  90 85 80 82 84 83 Average recovery  95 9188 91 88 89 rate/% Variation  5.263158 6.077348 9.090909 9.3922654.545455 6.214689 Example HF/HCl/HNO₃ Recovery rate (1)/%  97 95 91 9897 98 Recovery rate (2)/%  95 93 93 95 96 96 Average recovery rate/%  9694 92 97 97 97 Variation  1.041667 1.063830 1.086957 1.554404 0.5181351.030928 Mixed acid Metal to be quantitatively analyzed Mo W Tl Nb TaComparative Example HF/HNO₃ Recovery rate (1)/% 56 42 73 63 57 Recoveryrate (2)/% 65 50 99 80 78 Average recovery 61 46 86 72 68 rate/%Variation 7.438017 8.695652 15.116279 11.888112 15.555556 ComparativeExample HF/HCl/H₂O₂ Recovery rate (1)/% 83 71 93 89 82 Recovery rate(2)/% 81 70 91 92 86 Average recovery 82 71 92 91 84 rate/% Variation1.219512 0.709220 1.086957 1.657459 2.380952 Example HF/HCl/HNO₃Recovery rate (1)/% 93 80 96 96 90 Recovery rate (2)/% 100 81 96 93 99Average recovery rate/% 97 81 96 95 95 Variation 3.626943 0.6211180.000000 1.587302 4.761905

5. Quantitative Analysis of Metal Components by ICP-MS (2)

Table 2 and 3 below show quantitative analysis results (recovery rates,average of recovery rates and variation) obtained by performing, withnumber of times shown in Table 2 and 3 below, a process of subjectingthe susceptor treated by metal contamination of a known concentration inthe same way as in the 1 to processes of the 2 to 4, as to various metalcomponents shown in Table 2 and 3 below by the use of various kinds ofmixed acids shown in Table 2 and 3 below. Mixed acids shown in Table 2and 3 below are aqueous solutions containing acids shown in the Tablesas acid components and containing each acid in concentration shown inthe Tables.

TABLE 2 Recovery rate Recovery liquid Number of times Na Al Cr Fe Ni CuMo W Ti Nb Ta HF:H₂O₂ = 2%:2%  1  91%  87% 88% 87% 91% 95% 69% 52% 93%74% 95% (Comparative Example)  2  96%  98% 88% 94% 99% 91% 76% 48% 98%74% 98%  3  96%  92% 89% 85% 89% 92% 60% 40% 92% 72% 83%  4  98%  97%99% 96% 99% 92% 69% 37% 97% 67% 86%  5  90%  85% 86% 81% 85% 86% 59% 39%94% 71% 87%  6  90%  92% 80% 87% 87% 72% 64% 34% 98% 80% 71%  7  92% 89% 87% 89% 92% 93% 53% 35% 90% 63% 86%  8  78%  87% 75% 86% 78% 83%71% 42% 89% 69% 91%  9 100%  96% 98% 97% 96% 98% 61% 41% 96% 75% 93% 10 96%  94% 85% 88% 94% 91% 65% 47% 98% 61% 83% Average  93%  92% 88% 89%91% 89% 65% 42% 94% 71% 87% Variation  11.81025  7.523192 13.43561 9.212123 11.79414 14.65606 17.92586 21.62347  4.503831 13.48665 15.4867HF:H₂O₂ = 18%:18%  1  91%  95% 93% 95% 87% 97% 94% 76% 99% 95% 93%(Comparative Example)  2  99%  95% 90% 91% 92% 92% 85% 61% 95% 87% 95% 3  94% 100% 91% 85% 87% 86% 77% 67% 99% 80% 92%  4  93%  99% 91% 87%92% 84% 84% 69% 96% 91% 96% Average  94%  97% 91% 89% 89% 90% 85% 69%97% 88% 94% Variation  4.230685  2.386234  1.817159  5.558101  2.974665 7.018923 10.42471 11.02422  2.185086  8.171128  1.62415 HCl:H₂O₂ =2%:2%  1  73%  68% 63% 64% 70% 64% 52% 25% 83% 64% 44% (ComparativeExample)  2  90%  89% 83% 76% 84% 86% 50% 25% 85% 62% 43% Average  81% 79% 73% 70% 77% 75% 51% 25% 84% 63% 43% Variation  10.70643  13.3799913.53577  9.206073  9.408594 14.8169  1.804632  0.19425  1.331291 2.139104  1.322807 HF:HNO₃ = 2%:2%  1  72%  78% 71% 74% 73% 70% 56% 42%73% 63% 57% (Comparative Example)  2  91%  93% 86% 87% 87% 86% 65% 50%99% 80% 78% Average  82%  86% 79% 80% 80% 78% 61% 46% 86% 72% 67%Variation  11.85557  8.317268  9.536486  8.099624  8.590793 10.31672 7.393014  8.732303 15.37552 11.40898 15.42041 HF:HNO₃ = 2%:63%  1  97% 97% 93% 94% 89% 87% 76% 57% 93% 83% 90% (Comparative Example)  2  95% 73% 91% 92% 83% 64% 87% 65% 94% 93% 90%  3  72%  72% 69% 76% 68% 58%72% 57% 80% 75% 89%  4  89%  77% 91% 90% 83% 57% 81% 61% 98% 93% 93%Average  88%  80% 86% 88% 81% 66% 79% 60% 91% 86% 91% Variation 14.43056  15.86977 13.96839  9.845738 13.03433 22.52942  8.913299 6.491822  9.760876 10.52831  2.478012 HCl:HNO₃ = 15%:17%  1  88%  96%89% 92% 90% 74% 70% 49% 29% 29% 42% (Comparative Example)  2  83%  100%86% 87% 92% 87% 55% 43% 20% 20% 46% Average  86%  98% 87% 90% 91% 81%62% 46% 24% 24% 44% Variation  2.783534 2.162472  1.668322  2.50828 1.231021  8.365455 11.84759 6.957114 19.04637 19.02423  3.910303HCl:HNO₃ = 5%:51%  1  67%  75% 70% 68% 44% 74% 61% 38% 29% 28% 27%(Comparative Example)  2  86%  95% 85% 81% 57% 93% 72% 52% 23% 25% 32%Average  76%  85% 77% 75% 51% 83% 67% 45% 26% 27% 30% Variation 12.87928  11.91481  9.661576  8.57539 11.91922 11.63275  8.66407215.01884 11.82173  6.452176  7.511449 HF:HCl:H₂O₂ = 4%/3%/3%  1  99% 83% 94% 99% 99% 98% 84 % 70 % 93% 89% 93% (Comparative Example)  2  99% 88% 96% 99% 92% 94% 73% 76% 93% 74% 82%  3  98%  85% 81% 92% 96% 94%88% 69% 94% 92% 83%  4  90%  85% 80% 82% 84% 83% 61% 60% 81% 72% 86%Average  97%  85% 88% 93% 93% 92% 77% 69% 90% 81% 86% Variation 4.843423 2.607979  9.477608  9.237332  8.028521  8.296885 17.31926 11.6246 7.422523 12.15215  6.368361

TABLE 3 Recovery rate Recovery liquid Number of times Na Al Cr Fe Ni CuMo W Ti Nb Ta HF:HCl:HNO₃ = 8%/12%/14%  1 95%  91% 99%  93%  99%  97% 95% 84% 93%  94% 100% (Example)  2 98%  94% 99%  99%  99%  92%  89% 80%91%  83%  92%  3 95% 100% 95%  96%  96%  91%  83% 73% 95%  87%  91%  499%  93% 98%  98%  93%  91%  87% 78% 94%  90%  97%  5 97%  90% 91%  98% 90%  91%  93% 80% 90%  86%  90%  6 92%  91% 96%  99%  97%  95%  94% 84%91%  99%  96%  7 93%  94% 99%  94%  98%  92%  83% 75% 99%  84%  98%  899%  99% 98%  93%  91%  96%  85% 77% 97%  97%  92%  9 95%  93% 93%  95% 92%  91%  89% 78% 98%  93%  99% 10 99% 100% 95%  96%  91%  92%  93% 76%96%  94%  96% Average 96%  94% 96%  96%  95%  93%  89% 78% 94%  91%  95%Variation  3.738757  4.984849  4.094723  3.11877  4.647783  3.209129 6.955777  7.181595  5.022953  8.640351  4.794561 Recovery rate Recoveryliquid Number of times Li Mg K Ca V Mn Co Zn Sr Ag Ba Pb HF:HCl:HNO₃ =8%/12%/14%  1 92%  96% 94%  95% 109%  96%  95% 92% 94%  98%  98% 83%(Example)  2 89%  94% 88% 100%  99%  93%  93% 91% 94%  96%  98% 86%  388%  93% 89%  95%  99%  94%  95% 93% 95%  93% 100% 89%  4 87%  91% 87% 97%  93%  92%  93% 93% 93%  95%  98% 89%  5 97%  98% 95%  99%  97%  98% 97% 80% 92%  94%  94% 96%  6 95%  98% 97%  93%  92% 100%  99% 78% 90% 91%  90% 99%  7 94% 100% 93%  85%  98%  99%  94% 90% 91%  98%  94% 92% 8 97%  96% 97%  86%  99% 100%  94% 91% 91%  96%  92% 98%  9 99%  91%94%  93% 100%  95% 100% 95% 95%  95%  97% 92% 10 99%  95% 96%  94%  99% 95%  97% 91% 94% 100%  96% 94% Average 94%  95% 93%  93%  99%  96%  96%89% 93%  96%  96% 92% Variation  6.682799  4.522123  5.368057  7.763752 8.806553  3.823727  3.6461  9.552607  2.703794  4.56831  4.956766 8.699784

From the comparison between Examples and Comparative Examples shown inTables 1 to 3, it can be confirmed that, in Examples, various metals canbe recovered at a higher recovery rate (various metals can be recoveredat an average recovery rate exceeding 75%) and variation in measurementresults is smaller (variation lower than 10% as to various metals) bythe use of a mixed acid of hydrofluoric acid, hydrochloric acid andnitric acid as the recovery liquid, than in Comparative Examples.

In addition, ICP-MS used for quantitative analysis in Examples is anapparatus capable of performing high-sensitive quantitative analysis.With ICP-MS, even a slight metal contamination would be able to bedetected and quantitatively analyzed.

From the above results, it can be confirmed that, in Examples,cleanliness of a silicon carbide-based member was able to be highlyaccurately analyzed.

The SRc (average peak height of roughness curved surface) and the SPc(average peak height of cross-section curved surface) of the siliconwafer-placing surface of the susceptor for which the evaluation wasperformed were measured at four positions. Measurement results are shownin Table 4 below.

TABLE 4 SRc (μm) SPc (μm) Measurement position 1 1.73 1.73 Measurementposition 2 6.71 6.71 Measurement position 3 1.85 1.85 Measurementposition 4 2.74 2.74

An aspect of the present invention is useful in a field of manufacturinga silicon wafer.

1. A method of determining a cleaning condition of a member having asilicon carbide surface, the method comprising: cleaning the siliconcarbide surface under a candidate cleaning condition; after thecleaning, evaluating the cleanliness of the member having the siliconcarbide surface by a method comprising: bringing the silicon carbidesurface into contact with a mixed acid of hydrofluoric acid,hydrochloric acid, and nitric acid; concentrating the mixed acid broughtinto contact with the silicon carbide surface by heating to obtain aconcentrated liquid; adding a solution to the concentrated liquid toobtain a sample solution; performing quantitative analysis of metalcomponents present in the sample solution by Inductively CoupledPlasma-Mass Spectrometry; and evaluating cleanliness of the memberhaving the silicon carbide surface on the basis of a quantitative resultof the metal components obtained by the quantitative analysis; anddetermining that the candidate cleaning condition under which thecleanliness of the member having the silicon carbide surface has beenevaluated to be within an allowable level is to be used as a cleaningcondition of the member having the silicon carbide surface used in anactual manufacturing process of a silicon wafer.
 2. The method accordingto claim 1, wherein in the mixed acid, a concentration of hydrofluoricacid ranges from 5 to 15 mass %, a concentration of hydrochloric acidranges from 5 to 15 mass %, and a concentration of nitric acid rangesfrom 5 to 15 mass %.
 3. The method according to claim 1, wherein thesolution added to the concentrated liquid is an aqueous solution ofhydrofluoric acid and hydrogen peroxide.
 4. The method according toclaim 1, wherein the member having the silicon carbide surface is amember for manufacturing a silicon wafer.
 5. The method according toclaim 4, wherein the member for manufacturing a silicon wafer is asusceptor.
 6. A method of manufacturing a silicon wafer, the methodcomprising: determining a cleaning condition of a member having asilicon carbide surface by the method according to claim 1; cleaning themember for manufacturing a silicon wafer having the silicon carbidesurface under the determined cleaning condition; and manufacturing asilicon wafer through a manufacturing process that uses the cleanedmember.
 7. The method according to claim 6, wherein in the mixed acid, aconcentration of hydrofluoric acid ranges from 5 to 15 mass %, aconcentration of hydrochloric acid ranges from 5 to 15 mass %, and aconcentration of nitric acid ranges from 5 to 15 mass %.
 8. The methodaccording to claim 6, wherein the solution added to the concentratedliquid is an aqueous solution of hydrofluoric acid and hydrogenperoxide.
 9. The method according to claim 6, wherein the member havingthe silicon carbide surface is a member for manufacturing a siliconwafer.
 10. The method according to claim 9, wherein the member formanufacturing a silicon wafer is a susceptor.
 11. A method ofmanufacturing a silicon wafer, the method comprising: evaluatingcleanliness of a member for manufacturing a silicon wafer having asilicon carbide surface by a method comprising: bringing the siliconcarbide surface into contact with a mixed acid of hydrofluoric acid,hydrochloric acid, and nitric acid; concentrating the mixed acid broughtinto contact with the silicon carbide surface by heating to obtain aconcentrated liquid; adding a solution to the concentrated liquid toobtain a sample solution; performing quantitative analysis of metalcomponents present in the sample solution by Inductively CoupledPlasma-Mass Spectrometry; and evaluating the cleanliness of the memberhaving the silicon carbide surface on the basis of a quantitative resultof the metal components obtained by the quantitative analysis; andmanufacturing a silicon wafer through a manufacturing process that usesthe member whose cleanliness has been determined to be within anallowable level as a result of the evaluation.
 12. The method accordingto claim 11, wherein in the mixed acid, a concentration of hydrofluoricacid ranges from 5 to 15 mass %, a concentration of hydrochloric acidranges from 5 to 15 mass %, and a concentration of nitric acid rangesfrom 5 to 15 mass %.
 13. The method according to claim 11, wherein thesolution added to the concentrated liquid is an aqueous solution ofhydrofluoric acid and hydrogen peroxide.
 14. The method according toclaim 11, wherein the member having the silicon carbide surface is amember for manufacturing a silicon wafer.
 15. The method according toclaim 14, wherein the member for manufacturing the silicon wafer is asusceptor.